To meet the demand for wireless data traffic having increased since deployment of 4G (4th-Generation) communication systems, efforts have been made to develop an improved 5G (5th-Generation) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’. The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access(NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of Things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “Security technology” have been demanded for IoT implementation, a sensor network, a Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing Information Technology (IT) and various industrial applications.
In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as a sensor network, Machine Type Communication (MTC), and Machine-to-Machine (M2M) communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud Radio Access Network (RAN) as the above-described Big Data processing technology may also be considered to be as an example of convergence between the 5G technology and the IoT technology.
Currently, long term evolution (LTE) technology is being widely implemented by wireless communication systems. In LTE, without discontinuous reception (DRX), a user equipment (UE) has to be awake all the time in order to decode downlink data, as the data in the downlink may arrive at any time. This means that UE has to monitor the physical downlink control channel (PDCCH) in every sub-frame to check if there is downlink data available. This has serious impact on the power consumption of the UE. However in presence of the DRX, the UE discontinuously monitors the PDCCH. The occasions of monitoring PDCCH are configured by the base station (or eNodeB) using multiple timers as illustrated in FIG. 1. The timers include an on duration timer that indicates the time that the UE remains in DRX active state after start of DRX cycle. Further, a drx-Inactivity timer indicates the time that the UE remains in DRX active state after receiving a PDCCH with downlink control information (DCI) indicating new transmission. A drx-Retransmission timer indicates the time that the UE remains in DRX active state to receive PDCCH for retransmission scheduling. A ra-Response timer indicates a time for which the UE is in active state after transmission of Random Access Preamble. A mac-Contention resolution timer indicates a time for which the UE is in active state after transmission of Msg-3. Further, a drxCycle indicates a cyclic timer (which is restarted at each expiry point) indicating the DRX cycle. A drxCycleTimer indicates that at the end of this timer, the UE switches from a short DRX cycle (i.e. short drxCycle value) to a long DRX cycle (i.e. long drxCycle value). Further, a drxStartOffset indicates the starting sub-frame offset of the DRX cycle.
In an example scenario, consider a cellular internet of things (IoT) environment, it is expected that because of increased repetition, physical downlink control channel (PDCCH), physical downlink shared channel (PDSCH) and physical uplink shared channel (PUSCH) transmissions may extend more than 1 sub-frame. Also, scheduling gap of more than 1 sub-frame may exist between end of PDCCH transmission and start of corresponding scheduled PDSCH/PUSCH transmission. FIG. 2 illustrates a PDCCH scheduling gap, where PDCCH-1 provides scheduling information of PDSCH-1; PDCCH-2 provides scheduling information of PDSCH-2, and so on. These factors render the current procedure of DRX operation ineffective for cellular IoT. Hence, new mechanism needs to be defined for the DRX operation for cellular IoT.